Inkjet recording methods, which enable simple and inexpensive image formation, have been used in various printing fields. As one type of inkjet inks, there have been known inks that contain a photocurable compound to be cured by irradiation with actinic radiation (hereinafter, simply referred to as “actinic radiation curable inks”).
Recently, there have been developed actinic radiation curable inks that contain a gelling agent and undergo temperature-induced sol-gel phase transition (hereinafter, simply referred to as “gel inks”). The gel ink is warmed to be a sol and can be ejected from a nozzle of an inkjet head. After ejection, the ink is cooled to be gelled when landed on a recording medium, and thus is characterized by having a high pinning property after landing. Irradiating the gel ink pinned on the surface of the recording medium with actinic radiation causes the gel ink to be cured on the surface of the recording medium to thereby form an image.
There have been researched various techniques to form a desired image using gel inks. For example, PTL 1 describes a method in which the quality of an image to be formed is adjusted depending on a substrate by adjusting the viscosity of a gel ink landed on the substrate by preheating the substrate in order to control spreading of droplets of the ink. PTL 2 describes a method in which a gel ink landed on a less flat substrate such as a corrugated board is irradiated with ultraviolet radiation while planarized by pressure from a transparent nip to thereby level the height of a cured film to be formed on the substrate. In the method described in PTL 2, which is a method used for printing on a less flat surface such as an outer layer of a corrugated board, it is conceived that planarizing the surface of a cured film increases the gloss.
PTL 3 mentions that a polyethylene terephthalate (PET) substrate is subjected to corona discharge treatment before formation of an image by use of gel inks. The corona discharge treatment on the substrate that is performed in PTL 3 is conceived to be performed for improving the leveling property of the ink landed.
PTL 4 discloses an inkjet recording method by which an image having a uniform gloss without sense of incongruity can be obtained on a non-absorptive or slightly absorptive substrate by use of gelling agent-containing actinic radiation curable inkjet inks, with which the glossiness of an image to be formed changes depending on a difference in temperatures of recording media.